On 2012-01-08 09:24:21 +0000, Richard Fateman said:
> Plot[Cos[1.0 + n*2.0^-47], {n, -5, 5}] looks empty
>
> Plot[Cos[1.02 + n*2.0^-47], {n, -5, 5}]
> looks like a straight line with slope about -1
>
> version 7
This is due to what I think are some deceptive plotting defaults in
Mathematica. Where the axes cross is not necessarily the origin; not in this
case, at any rate. I think it would be a lot clearer if the x-axis in
this case were either plotted in dashed form or grayed out a little bit
more, to show its not at its expected position, y = 0.
If you specify that the axes must cross at the origin, you'll see that
in both cases the slope was tiny, nowhere near what it looked like:
Plot[Cos[1. + n/2.^47], {n, -5, 5},
PlotStyle -> {Red, Thick},
AxesStyle -> Lighter[Blue, 0.7],
AxesOrigin -> {0, 0}
]
Plot[
Cos[1.02 + n/2.^47], {n, -5, 5},
PlotStyle -> {Red, Thick},
AxesStyle -> Lighter[Blue, 0.7],
AxesOrigin -> {0, 0}
]